
Flesch-Kincaid formula (F-K): the weighted sum of the number of words in a sentence and the number of syllables per word [1]},

Coleman-Liau index (CL): the weighted sum of the number of letters per 100 words and the average number of sentences per 100 words [2]},

SMOG: the weighted square root of the number of polysyllable words per sentence [3]}, and

Automated readability index (ARI): the weighted sum of the number of characters per word and number of words per sentence [4]}.

